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[2003:cb:c71c:a700:bba7:849a:ecf1:5404]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-434aa74f2c7sm85744075e9.2.2024.11.29.05.12.23 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 29 Nov 2024 05:12:24 -0800 (PST) Message-ID: Date: Fri, 29 Nov 2024 14:12:23 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] perf: map pages in advance To: Lorenzo Stoakes Cc: Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , Alexander Shishkin , Jiri Olsa , Ian Rogers , Adrian Hunter , Kan Liang , linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Matthew Wilcox References: <20241128113714.492474-1-lorenzo.stoakes@oracle.com> <9f9fd840-6421-43b5-9a12-edfa96e067cc@redhat.com> <1af66528-0551-4735-87f3-d5feadadf33a@lucifer.local> <926b3829-784f-47b8-9903-ea7b9ad484ac@redhat.com> <31e8202d-f3db-4dcd-a988-2f531b14e40f@lucifer.local> <84fed269-3f82-47f7-89cb-671fcee5a23a@redhat.com> <20241129122624.GH24400@noisy.programming.kicks-ass.net> <74be541b-22ad-42b5-b3c5-79b201e28f04@redhat.com> <9d6be5bd-ffb9-4a27-b56d-521cf6b7486e@redhat.com> <6cab3e8a-dff7-41d1-af22-f18b8f2820dc@lucifer.local> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 29.11.24 14:02, Lorenzo Stoakes wrote: > On Fri, Nov 29, 2024 at 01:59:01PM +0100, David Hildenbrand wrote: >> On 29.11.24 13:55, Lorenzo Stoakes wrote: >>> On Fri, Nov 29, 2024 at 01:45:42PM +0100, David Hildenbrand wrote: >>>> On 29.11.24 13:26, Peter Zijlstra wrote: >>>>> On Fri, Nov 29, 2024 at 01:12:57PM +0100, David Hildenbrand wrote: >>>>> >>>>>> Well, I think we simply will want vm_insert_pages_prot() that stops treating >>>>>> these things like folios :) . *likely* we'd want a distinct memdesc/type. >>>>>> >>>>>> We could start that work right now by making some user (iouring, >>>>>> ring_buffer) set a new page->_type, and checking that in >>>>>> vm_insert_pages_prot() + vm_normal_page(). If set, don't touch the refcount >>>>>> and the mapcount. >>>>>> >>>>>> Because then, we can just make all the relevant drivers set the type, refuse >>>>>> in vm_insert_pages_prot() anything that doesn't have the type set, and >>>>>> refuse in vm_normal_page() any pages with this memdesc. >>>>>> >>>>>> Maybe we'd have to teach CoW to copy from such pages, maybe not. GUP of >>>>>> these things will stop working, I hope that is not a problem. >>>>> >>>>> Well... perf-tool likes to call write() upon these pages in order to >>>>> write out the data from the mmap() into a file. >>> >>> I'm confused about what you mean, write() using the fd should work fine, how >>> would they interact with the mmap? I mean be making a silly mistake here >> >> write() to file from the mmap()'ed address range to *some* file. >> > > Yeah sorry my brain melted down briefly, for some reason was thinking of read() > writing into the buffer... > >> This will GUP the pages you inserted. >> >> GUP does not work on PFNMAP. > > Well it _does_ if struct page **pages is set to NULL :) Hm? :) check_vma_flags() unconditionally refuses VM_PFNMAP. -- Cheers, David / dhildenb